Method of heat-treating cutting tools



A. E. BELLIS METHOD OF HEAT TREATING CUTTING TOOLS Filed Sept. 8, 1923INVENTOR JZrZZzuLEZ BYC ATTOQN Y'- Patented Feb. 17, 1925.

V UNITED STATES A 1,526,894 PATENT OFFICE.

ARTHUR E. BELLIS, OF' NEW HAVEN, CONNECTICUT, ASSIGNOR T BELLIS HEATTREATING COMPANY, OF BRANFO-RD, NECTICUT.

CONNECTICUT, A CORPORATION OF CON- METHOD OF HEAT-TREATING CUTTING-TOOLS.

Application filed September 8, 1923. Serial No. 661,558.

To all whom it may concern.-

Be it known that I, ARTHUR E. BELLIS, a citizen of the United States,and a resident of New Haven, county of New Haven,

and State of Connecticut, have invented cer-- tain new and usefulImprovements in Methods of Heat-Treating Cutting Tools, of

which the following is a specification.

This invention relates to an improved methodpf heat treating cuttingtools and in its broader aspect, contemplates the heat treatment of thetool in such manner that maximum hardness of all parts of the cuttingpoint or points of the tool is secured,

while other portions of the tool possess a high degree of toughness andresistance to tensile strains.

In the heat treatment of cutting tools and particularly, high speedtools such as rock drills, it has heretofore been the general practiceto subject the tool to immersion in a lead bath or to treatment in amuffle furnace. In the lead bath treatment, owing to the relatively highviscosity of the lead,

there is an unequal distributiomof heat and different parts of the toolwhich it is desired to subject to the same heat treatment, are heated torelatively different temperatures. Likewise, in the use of a mufflefurnace, it

has been found exceedingly diflicult, if not impossible, to secure auniform heating of the different parts of the tool.

By means of my improved method, to be hereinafter described in detail,"I am en- 85 abled to subject different portions of the tool element toheat treatment for relatively different periods of time and secure anabsolutely uniform temperature of all parts of the different sections orportions of the 4.0 tool, so that a desired degree of hardness may beobtained in different portions of the tool, as for instance, the cuttingpoint or points, while the remaining portions of the tool may be treatedso as to secure maximum toughness or tensile strength thereof-z To thisend, in carrying out my improved method, I employ a bath, consisting ofchemical salts capable of being heated to a relatively high degreewithout volatilization. In a bath of this character, the cutting ointsof the tool are first immersed and t e remaining portion of the tool isthen slowly immersed in the bath so that such portion of the tool issubjected to the heat period of time, will be of less hardness, but

very tough and capable of resisting high tensile strains.

I have found the improved method particularly advantageous in the heattreatment of rock drills for the purpose ofsex curing maximum hardnessand resistance to frictional wear of the bit points of thedrill whilethe pilot end of the drill which is mounted in the rotary cutting headwill be of great tensile strength. It has been found that drills thustreated require resharpening only at relatively infrequent intervals,the cutting edges of the bit points retaining their sharpness for arelatively long period of time. While I have referred to' the inventionas especially adapted for the heat treatment of rock' drills, it willwise be advantageously employed in the heat treatment of cutting toolsemployed for various other purposes where maximum hardness of thecutting point with a high degree of tensile strength in the other partsof the tool is required.

In the accompanying drawing I have illustrated a conventlonal type ofrock-drill, the illustrated example showing the drill body 5 providedwith a bit having four diametrically extending cutting points 6 at oneof its ends. The body 5 at its opposite end is formed with the threadedpllot shank 7 whereby the drill is connected to the rotary cutting headin the usual manner. The specific tool which I have selected forpurposes of illustration constitutes no essential part of the presentinvention, and it will, therefore, be understood that my improved methodof heat treatment may be applied in connection with tools of varioussizes and shapes provided with a greater or. less various other salts.

number of the cutting points and used for a variety of differentpurposes.

In one practical embodiment of my invention I provide a salt bath, suchfor instance as that disclosed in my Patent, No. 1,491,510, issued April22, 1924, the said bath preferably consisting of an eutectic mixture ofa plurality of salt components.

One characteristic bath may consist of sodium chloride (NaCl) and sodiumcarbonate (Na GO in such relative proportions that the mixture has amelting point less than that of the individual salt components and avolatilization tem erature of approximately 1600 F. The me ting pointtemperature and the volatilization temperature will of course, vary inaccordance with relative proportions of the salt components. I have alsofound it advantageous in many cases to use chromium salts in place ofthe chloride and it will, therefore, be understood that the abovereference to a particular salt bat-h composition implies no limitationsas the bath might be prepared from It is, however, an essentialcharacteristic of the bath that it has very low viscosity and,therefore, rapid heat conductivity so that all parts of the bathsolution are uniformly heated to the same temperature.

In the heat treatment of rock-drills such as that illustrated in thedrawing, for a drill having a carbon oontentl of .40 of 1% or greater,the bath is heated to a temperature of approximately 1520 F. andmaintained at such temperature during the entire heat treatment period.The cutting points of the drill bit are then immediate- 1y immersed inthe bath solution from the cutting edges thereof to a pointsubstantially-that indicated by the line B in the drawing. The immersionof the bit is then slowly continued so that approximately 110 seconds isconsumed in the immersion of the bit to the point indicated by the lineC, it being noted that this portion of the immersion movement includesthe main body part of the bit. The remainder of the bit, consisting ofthe pilot shank 7, is then immediately immersed and allowed to remain inthe bath for a. period of ten seconds. It will thus be apparent that thewhole period of heat treatment extends through approximately two minutesafter which the tool is immediately withdrawn and quenched in Water.After quenching of the tool, the pilot end 7 thereof is immersed in abath similar to that above referred to having a temperature of 700 F.for a period of two minutes to draw the temper of the metal.

After the tool has been treated in the manner above described, it willbe found by test that the bit pgoints 6 of the tool be-' tween lines Aand have a hardness of 90 schleroscope While the body portion of aeaaeeethe-tool between the lines B and C has a hardness varying from 90 to 55schleroscope While the remaining pilot end portion of the tool betweenthe lines C and D has a hardness of 55 schleroscope. It will of coursebe apparent that these stated degrees of hardness are only approximateand that it is not to be expected in the operation of the improvedmethod, that variations thereof will not occur. Indeed, in some cases itmight be found desirable to increase or decrease the hardness of thedifferent portions of the tool by subjecting the same to the heattreatment temperature in the bath solution for greater or less periodsof time than those stated.

However, in general practice it has been found that substantially thestated degrees of hardness of the different parts of the tool give thebest results particularly in the operation of rock-drills, which, as iswell known, are frequently subjected to very severe usage. By reason ofthe fact that the heat treatment of the different parts of the tooloccurs in a bath of, low viscosity, all parts of the bit points Will beheated to precisely the same temperature and will, therefore, possessexactly the same degree of hardness throughout their structure. The sameis-also true of the intermediate body section of the tool and of thepilot end portion. It is also a characteristic feature of the bath thatwhen the tool is withdrawn therefrom all of the surfaces are coveredwith a film of the bath material which affords a complete protectionagainst oxidization from the atmosphere. As this bath solution does notpossess the tenacity of a lead bath, it will not adhere to the metalsurface at spaced points and thus subject certain portions of .the toolto prolonged heating. 7

Accordingly, it will be seen that by means of my improved method thenecessity of regrinding or sharpening the bit points at more or lessfrequent intervals is, to a certain extent, obviated and the drill maybe continuously used for a relatively long period of time withoutrequiring re-sharpening. Also, by the uniform heat treatment of thepilot end of'the drill for a shorter period of time, a uniformly toughhomogeneous structure thereof is obtained which will offer maximumresistance to tension or torsional strains.- Accordingly it will beappreciated that by heat treating the drills in accordance with mypresent invention,

the maintenance and operating cost of rock U remaining portions of thetool in thebath for varying periods of time so that when the tool iswithdrawn from the bath and quenched, the cutting part thereof willpossess a higher degree of hardness than the remaining portions of thetool.

2. In the art of heat treating cutting tools, that step which consistsin quickly ii'nmersing the entire cutting part of the tool in a fusedsalt bath and then slowly continuing the immersion ,of an intermediateportion of the tool during a definite period of time and finally quicklyimmersing all of the remaining portion of the tool where by when thetool'is withdrawn from the bath and quenched, the cutting part thereofwill possess the greatest degree of hardness, while the other portionsof the tool .will

successively decrease in hardness.

3. In the art of heat treating cutting tools, that step which consistsin quickly immersing the entire cutting part of the tool in a fused saltbath maintained at a constant temperature, and then slowly con-' tinuingthe immersion of an intermediate portion of the tool during a definiteperiod of time and finally, quickly immersing all of the remainingportion of the tool whereby when the toolis withdrawn from the bath andquenched, the cutting part thereof will possess the greatest degree ofhardness, while the other portions of the tool will suecessivelydecrease in hardness.

4. In the art of heat treating cutting tools, that step which consistsin quickly immersing the entire cutting part of the tool in a fused saltbath having a temperature of approximately 1520 F., and then slowlycontinuing the immersion of an intermediate portionof the tool during adefinite period of time and finally, quickly immersing all of theremaining portion of the tool whereby when the tool is withdrawn fromthe bath and quenched, the cutting part thereof will possess thegreatest degree of hardness, while the other portions of the tool willsuccessively decrease in hardness.

5. The method of heat treating rock drills having a cutting bit at oneend and a pilot at the other end whichconsists in quickly immersing thecutting parts of the bit in a fused salt bath maintained at a constanttemperature and then slowly continuing the immersion of the intermediatebody section of the tool through a definite period of time and thenfinally, quickly immersing the pilot end of the tool and subjecting thesame to the'temperature of the bath solution for a relatively shortperiod of time, whereby, when the tool is withdrawnfromthe bath andquenched, the cutting parts thereof will possess the greatest degree ofhardness while the intermediate and pilot end portions of and thenfinally, quickly immersing the pilot end of the tool and subjecting thesame to the temperature of the bath solution for a relatively shortperiod of time, whereby when the tool is withdrawn from the bath andquenched, the cutting parts thereof will possess the greatest degree ofhardness while the intermediate and pilot end portions of the tool willgradually decrease in hardness, and thereafter drawing the temper of thepilot end of the tool by immersing the same in a salt bath ofrelativelylow temperature fora period of two minutes.

7. The method f heat treating rock drills having a cutting bitat one endand a pilot atthe other end which consists in quickly immersing thecutting parts of the bit in a fused salt bath having a temperature ofapproximately 1520 F. and then slowly continuing the immersion of theintermediate body section of the tool through a definite period of timeand then, finally quickly immersing the pilot end of the tool andsubjecting the same to the temperature of the bath solution for arelatively short period I same in a salt bath having a temperature ofapproximately 700 F. for aperiod of two minutes. i I

In testimony that I claimthe foregoing as my invention, I have signed myname hereunder.

ARTHUR E. BELLIS.

